18 



DIGESTION. 



cil ihe. aiient to this purpose, has led to many 

 singular theoretical opinions, which will he 

 noticed in a subsequent part of this article.* 



But in whatever way, or upon whatever 

 principle we may explain the action of the 

 gastric fluid upon the aliment, we are irre- 

 sistibly led to the conclusion, that it is the 

 physical agent which produces the effect, not 

 only from those cases, where in consequence 

 of a preternatural opening into the stomach 

 we are able to observe the actual phenomena 

 of digestion, but still more so, by the expe- 

 riments on what has been termed artificial di- 

 gestion, especially those of Spallanzani and 

 lieaumont, where the gastric juice has been 

 procured, and applied out of the stomach, 

 and where the process of chymification has 

 proceeded, as nearly resembling that in the 

 stomach itself as might reasonably be ex- 

 pected, considering the unavoidable imper- 

 fection of the experiment. This imperfection 

 respects both the mode of obtaining the gastric 

 juice itself, and the mode of applying it to 

 the aliment. We reduce the action of the 

 stomach into somewhat of an unnatural con- 

 dition in order to procure the secretion, and 

 in the application of it we are deprived of the 

 contractile motion of the organ; yet, not- 

 withstanding these unavoidable circumstances, 

 the substances were reduced to a state very 

 considerably resembling that of chyme. That 

 this change was not produced by a mere me- 

 chanical action is proved by the circumstance, 

 that the change in the substances operated on 

 bore no proportion to the hardness of their 

 texture or other physical properties. Thus we 

 find that the gastric fluid acts upon dense 

 membrane, and in some cases, even upon 

 bone, while there are other substances, of a 

 very delicate texture, which are not affected 

 by it. This kind of selection of certain sub- 

 stances in preference to others bears so close 

 an analogy to the operation of chemical affinity, 

 that we ought not to refuse our assent to the 

 idea of their belonging to the same class of 



tial agent in the process. From the first part of 

 this remark we must, however, except Vanhelmont 

 and Willis; Onus Mcd. p. 164 . .7 et alibi ; De 

 Ferment, op. t. i. p. 25. See Haller in Boerhaavc, 

 Pralcct. not. ad $ 77, and El. Phys. xix. 1. 15, 



i^VL 4 ' 2?,? F /? rdvcc > P- 150. 1 i Spallanzani', 

 $ 239 . . 245 ; Hunter, p. 293 ct seq. ; Circaud, ut 

 upra; Dumas, El. Phys. t. i. p.278..0; Tiede- 

 inann et Gmclin, Hecherchcs, t. i. p. 166, 

 7. It may be proper to remark that Leuret and 

 Lassaigne do not admit of the presence of this 

 acid ; they, on the contrary, suppose that the 

 gastric juice owes its acid properties to the lactic 

 acid; Rcchcrchcs Physiol. ct Chimiques, p. 114. 7- 

 Dr. Prout has, however, as we conceive, satisfac- 

 torily answered their objections to his experiments - 

 Ann. Phil. v. xii. p. 406. Dr.Carswell considers 

 acidity to be the essential and active plopertv 

 of the gastnc juice ; Pathol. Anat. fas. 5. 



Montegre has lately performed a series of ex- 

 periments, the results of which lead him to dcnv 

 the specific action of the gastric juice ; Exper. sur 

 la Digestion, p. 43, 4. Hut, notwi.hstanding the 

 apparent accuiacy with which they were conducted 

 . cannot but suspect some source of error, scoin? 

 l...w much they are at variance with all our othe? 

 information ou the suliject. 



actions, although it occurs under circum- 

 stances where we might not have expected to 

 find it. 



There are two other properties of the gastric 

 juice, besides its solvent power, which are at 

 least as dilHcult to account for, but of which 

 we seem to have very complete evidence, 

 its property of coagulating albumen, and that 

 of preventing putrefaction. It is the former 

 of these properties which we employ in mak- 

 ing cheese, cheese being essentially the albu- 

 minous part of milk, coagulated by means of 

 what is termed rennet, a fluid consisting of the 

 infusion of the digestive stomach of the calf. 

 This is unequivocally a chemical change, yet 

 it is very difficult to explain it upon any che- 

 mical principle, i. e. to refer this individual 

 case to any series of facts, with which it can 

 be connected.* We can only say in this 

 instance, as in so many others in the physical 

 sciences, that although the fact is clearly 

 ascertained, its efficient cause still remains 

 doubtful. 



We are compelled to make the same re- 

 mark with regard to the other property of the 

 gastric juice, to which we have referred above, 

 its antiseptic power. Of the fact, however, 

 we are well assured, both as occurring in the 

 natural process of digestion, and in the expe- 

 riments that have been made out of the body. 

 It is not uncommon for carnivorous animals 

 to take their food in a half putrid state, when 

 it is found that the first action of the gastric 

 j uice is to remove the fcetor ; and an effect of 

 precisely the same kind was noticed by Spal- 

 lanzani in his experiments. f Here again we 

 have a chemical change, the nature of which 

 we cannot explain; it is, however, a circum- 

 stance which may appear less remarkable, with 

 respect to the subject now under consideration, 

 because the action of antiseptics generally is 

 one which we find it difficult to refer to any 

 general principles. 



Respecting the process of chymification it 

 only remains for us to remark, that the con- 

 tractile action of the stomach is admirably 

 fitted to aid the chemical action of the secreted 

 fluids ; the vermicular motion of the organ has 

 the effect of keeping the whole of its contents 

 in a gradual state of progression from the 

 cardia to the pylorus, while, at the same time, 

 each individual portion of the aliment is com- 

 pletely mixed together, and brought into the 



* This difficulty appears to be increased by the 

 amount of effect which is produced by the very 

 small quantity of the agent ; Fordyce informs us, 

 that a very few grains of the inner coat of the 

 stomach, a very small proportion of which must 

 have consisted of the secretion, was capable, when 

 infused in water, of coagulating more than one 

 hundred parts of milk ; p. 57,9; 176 et scq. ; 

 Piout, Ann. Phil. v. xiii. p. 13 et seq. 



t Exper. $ 250..2 et alibi ; see also Hunter on the 

 Anim. (Econ. p. 204. Montegre does not admit 

 of this property, and would appear to doubt also 

 of the coagulating power of the gastric juice, p. 21 

 et alibi ; the same opinion is also maintained by 

 Dr. Thackrah, lect. p. 14 ; but it would require a 

 very powerful series of negative facts to controvert 

 the strong evidence that we possess ou this 

 subject. 



